Description:
LO can read files with "\x2e" (".") in defined names from an XLS file.  When saving the files to XLSX, those characters are replaced with "\x5f" ("_").  It may be an issue with the XLS import filter or the XLSX export filter.  Since the test files were generated using LibreOffice save as XLS, the XLS export filter does not exhibit the issue.

Steps to Reproduce:
Open attachment and save as XLSX, then try opening the file in Excel

Actual Results:
File opens

Expected Results:
Excel reports file is invalid


Reproducible: Always


User Profile Reset: Yes



Additional Info:
The XLS file has the correct defined name:

```js
> require("xlsx").readFile("locrash.xls")?.Workbook?.Names?.map(x => x.Name)
[ '_xlfn.UNICHAR' ]
```

The generated XLSX does not:

```js
> require("xlsx").readFile("locrash.xlsx")?.Workbook?.Names?.map(x => x.Name)
[ '_xlfn_UNICHAR' ]
```

(note that the "." was replaced with "_")